Why Is Moblin's X.Org Stack Faster Than In Ubuntu?

Canonical's Scott James Remnant recently set out to explore why X.Org started up so much faster on Moblin than on Ubuntu (particularly, the latest 9.04 development code). On an Atom-based netbook (the Dell Mini 9) he found it took Ubuntu's X Server about four seconds to start before the session manager was called. With Moblin on the same hardware it took just about a second and a half.

Scott began analyzing the X Server patch-set for Moblin, that included enabling UXA acceleration by default, avoiding duplicated saved hardware states, reducing the driver boot-time, and disabling other operations. However, Ubuntu already incorporated all of these patches besides using UXA acceleration. Ubuntu's X Server also has a few extra patches, but those didn't seem to impact the performance.